This invention relates to an energy absorber for absorbing energy of a vehicle or component of a vehicle or occupant of a vehicle in a crash situation so as to allow relatively gradual deceleration of the vehicle, component or occupant.
The invention is of particular, but not exclusive, utility in relation to so-called crashworthy seats for helicopters. In the typical scenario of a helicopter crash, impact with the ground is preceded by a substantially vertical drop, with the result that a seated occupant of a helicopter experiences high spinal loads and pelvic deceleration during such a crash due to the sudden arresting of vertical downward motion. It has long been recognised that spinal injuries to occupants of helicopters in such a crash scenario can be minimised by seat arrangements which limit the deceleration to which the seated occupant is subjected, relative to the helicopter, to a predetermined maximum, by allowing downward movement of the seated occupant relative to the helicopter, at the time of impact with the ground, under a restraining force which, over a limited range of such movement, is limited to a predetermined maximum. In practice, significant benefits, in the way of reduced injuries and reduced seriousness of injuries, can be afforded in this way in such crash situations even where the extent of such controlled vertical movement permitted by the crashworthy seat arrangement is quite limited.
Many different types of energy absorbers for such purposes have been proposed and manufactured. Many of these prior energy absorbers utilise plastic deformation of metal parts as a means of absorbing energy.
However, there still exists a need for an improved energy absorber which is better able than existing energy absorbers to meet one or more of the following desiderata:
The device should provide a predictable force versus deformation trace.
The rapid loading rate expected in crashes should not cause unexpected changes in the force versus deformation characteristic of the device.
The device should have the ability to sustain tension and compression to provide anti-rebound characteristics.
The device should be as light and small as possible.
The device should be economical.
The device should be capable of being relied upon to perform satisfactorily throughout the life of the product (a minimum of 10 years or 8000 flight hours) without requiring maintenance.
The device should not be affected by vibration, dust, dirt, temperature or other environmental effects.
The device should be protected from corrosion.
The device should not use friction as a major force component in the energy absorber, as friction can vary greatly over different environmental conditions, and thus greatly affect the performance of the energy absorber to the possible determent of the occupant of a seat fitted with such an energy absorber, for example.
When used in, for example, a crashworthy helicopter seat, the device should decelerate the occupant of such seat in the most efficient manner possible while keeping the loads to which the occupant is subject within the limits of human tolerance.
It is a further object of the invention to provide a reliable, efficient and cost-effective energy absorber.
In accordance with one aspect of the invention there is provided an energy absorber for absorbing energy of a vehicle or component of a vehicle or occupant of the vehicle in a crash situation so as to allow relatively gradual deceleration of the vehicle, component or occupant, the energy absorber including a first part, a second part and an elongate deformable member secured to the first part and extending through a deforming arrangement carried by the second part, whereby said elongate deformable member normally acts as a tie or strut between said first part and said second part but wherein the arrangement is such that, when the force acting between said first part and second part in a predetermined direction exceeds a predetermined amount, said elongate deformable member is thereby forced progressively through said deforming arrangement as the distance between said first part and said second part changes and the deformable member is thereby forced to undergo plastic deformation, whereby energy is absorbed, and wherein said deforming arrangement is such as to effect such plastic deformation substantially without changing the material cross sectional area of the deformable member.
According to another aspect of the invention there is provided a vehicle seat assembly including a seat mounting secured to or securable to, structure of the vehicle, a seat proper including one or more body supporting parts, the seat proper being mounted for guided movement relative to said structure and at least one energy absorber according to the first-mentioned aspect of the invention having said first part thereof connected to one of said seat mounting and seat proper and having said second part connected to the other of said seat mounting and said seat proper, whereby the energy absorber normally restrains movement of the seat proper relative to the seat mounting but, in a crash situation, can allow controlled movement of the seat proper relative to the seat mounting, whilst absorbing energy as the elongate deformable member is forced through the deforming arrangement or as the deforming arrangement is forced along the elongate deformable member.
The invention also extends to a vehicle, such as a helicopter, provided with a seat assembly in accordance with the invention.